1. Field of the Invention
The present invention relates to a production method of a composite molded article such as a steering wheel having a plastic layer on the inside of a surface layer, and a composite molded article obtained by the method.
2. Description of the Related Art
A method like that shown in FIG. 9 has been proposed as a production method of a wood grain steering wheel in which the surface layer is composed of a wood material, and which has a plastic core material inside. In this method, the divided bodies 53 and 53 having a roughly U-shaped cross-section formed by dividing portions of the steering wheel other than a core metal 54 into two parts are butt joined followed by adhering corresponding divided bodies 53 and 53 as well as the divided bodies 53 and 53, and the divided body 53 and the core metal 54. The divided body 53 is composed of a surface material 51 comprised of a wood material, and a plastic core material 52 formed on the inside of the surface material 51.
However, this method had the disadvantages described below as a result of integrating the divided bodies 53 and 53 using adhesive.
Namely, in the steering wheel that was produced, there was the problem of susceptibility to the occurrence of cracking along the adhered surfaces of corresponding divided bodies 53 and 53. For example, when the plastic core material 52 expands due to changes in the environmental temperature, stress is concentrated in the joined surfaces of the divided bodies 53 as shown in FIG. 10, and when this stress on the joined surfaces increases, crack 55 forms along the joined surfaces in the coating film on the surface of the steering wheel as shown in FIG. 11.
In addition, since the joined surfaces of corresponding divided bodies 53 and 53 require a certain degree of high adhesive strength, and an annealing step is required following adhesion in order to satisfy this level of adhesive strength, the number of adhesion steps increases and the time required for adhesion becomes longer. In addition, an adhesion jig is also required.
Moreover, since adhesive is used, a step is required for removing burrs of adhesive that have protruded onto the steering wheel surface after the adhesion steps.
The present invention provides a method for integrating divided bodies in this manner, such as a method in which divided bodies can be integrated without using adhesive during the production of a composite molded article such as a steering wheel having a plastic layer on the inside of a surface material, as well as a composite molded article obtained with this method.
In order to solve the above problems, the present invention provides a composite molded article comprising a plastic layer integrally welded on the inside of a surface material which is divided into a plurality of divided bodies.
In addition, the present invention provides a production method of a composite molded article comprising the steps of: providing a plurality of divided bodies, each of which comprises a surface material and a plastic layer provided on the inside of the surface material; and integrally welding the plastic layers of a plurality of divided bodies.
In the production method of a composite molded article, it is preferable for the plastic layers of the divided bodies to be integrally welded by vibration welding, ultrasonic welding or high-frequency welding.
In the composite molded article obtainable by the present invention, the divided bodies can be integrated into a single unit without the use of adhesive. Thus, since adequate joining strength can be obtained in the welding step alone, in addition to an annealing step required in the case of using an adhesive no longer being required, since a step for removing adhesive burrs is also unnecessary, the number of steps is reduced and the amount of time required for production is shortened. In addition, the resulting composite molded article has superior strength.
The composite molded article and its production method of the present invention can be preferably applied to a steering wheel. Namely, the present invention provides a steering wheel comprising: a core metal; a central core provided around the periphery of at least a portion of the core metal, and an outer shell provided around the periphery of the central core; wherein the outer shell comprises a plurality of divided bodies comprising a surface material and a plastic layer provided on the inside of the surface material, and the plastic layers of the plurality of the divided bodies are mutually integrally welded.
In addition, the present invention provides a production method of a steering wheel comprising the steps of: a) providing a plurality of divided bodies, each of which comprises a surface material and a plastic layer provided on the inside of said surface material; b) forming an outer shell by integrally welding said plastic layers of said divided bodies; c) providing a core metal to be arranged in said outer shell; and d) filling plastic between said outer shell and said core metal.
In the production method of a steering wheel, it is preferable the plastic layers of the divided bodies to be integrally welded by vibration welding, ultrasonic welding or high-frequency welding.
The steering wheel obtained according to the present invention has superior strength since the outer shell is formed by combining a plurality of divided bodies having the surface material and the plastic layer provided on the inside of the surface material, and mutually integrally welding the plastic layers of the plurality of divided bodies.